DE102015100757B3 - Module with stress-free attached MEMS device - Google Patents

Abstract

The invention relates to a module in which a MEMS component is connected to a carrier in a stress-free manner over a wide temperature range via mechanical connections. For this purpose, a mechanical connection comprises a compensation structure which bridges a horizontal offset of fixing points by a horizontal shoulder and whose temperature expansion coefficient is suitably selected.

Description

The invention relates to modules in which a MEMS device is fastened stress-free over a wide temperature range.

MEMS devices (MEMS = Micro-Electro-Mechanical System) comprise mechanically active structures that are often sensitive to mechanical stress. A MEMS component can be, for example, an electroacoustic converter which is fastened and interconnected together with an ASIC chip (Application Specific Integrated Circuit) on a support of a microphone module. The transducer can have a vibratable membrane and a back plate (English: back plate), which form two electrodes of a capacitor. Vibrations of the membrane relative to the back plate cause a time-varying capacity. By evaluating the capacity, eg. B. by an ASIC, a sound signal can be converted into an electrical signal.

The problem is that the carrier and the material of the transducer generally have different coefficients of thermal expansion (CTE). When the temperature changes, mechanical stresses are transmitted to the converter via the connections between the carrier and the converter. Mechanical stresses in the transducer prevent undisturbed working of the mechanical structures, so that temperature changes have a negative effect on the signal quality of the microphone.

Temperature-induced disturbances are not unique to microphones. In principle, all MEMS device, z. As well as pressure sensors or working with acoustic waves filter components affected.

The DE 10 2010 012 042 A1 discloses electrical modules with a carrier substrate and a chip, which is connected via a mechanically deformable electrical line with a lower rigidity than the chip to the carrier.

The DE 10 2007 025 992 A1 discloses MEMS modules with a MEMS chip and a carrier substrate, in which thermally induced voltages are reduced by means of a frame structure between chip and carrier substrate in the vertical direction.

The ongoing trend towards ever-increasing miniaturization, the z. As thinner MEMS device requires, amplifies this problem, because thinner component deform more under the influence of external forces.

The introduction of mechanical stresses in MEMS device could be reduced by soft, easily deformable spring elements as links between the carrier and MEMS device. Then, however, the mechanical stability of the connection would be reduced and corresponding modules could stress tests, z. As fall tests, no longer exist.

There is therefore a desire for modules that meet the contradictory requirements: mechanical stability with simultaneous stress-free attachment of the MEMS device and also allow further miniaturization without having to compromise on the signal quality.

For this purpose, a module as well as various advantageous properties, which can individually or in combination improve the module described below according to independent claim 1, are given below. Dependent claims indicate advantageous embodiments of the module.

The module comprises a carrier having a first temperature expansion coefficient K ₁ , a first attachment point and a second attachment point. The module further comprises a MEMS device with MEMS structures, a second temperature expansion coefficient K ₂ , which is different from the first temperature expansion coefficient K ₁ , a first attachment point and a second attachment point. Furthermore, the module comprises a first mechanical connection between the first attachment point of the carrier and the first attachment point of the component. In addition, the module has a second mechanical connection between the second attachment point of the carrier and the second attachment point of the device. The second mechanical connection has a compensation structure with a temperature expansion coefficient K _K. The two attachment points on the MEMS device have a horizontal distance d ₁ and the attachment points on the carrier have a horizontal distance d ₂ . The values for d ₁ and d ₂ are selected so that the compensation structure compensates for the different changes in length of d ₁ and d ₂ when the temperature changes, so that the MEMS component is connected to the carrier without voltage but at different temperatures.

It has been found that mechanical connections between the carrier and the device can be dimensioned and their material, in particular their coefficients of expansion, can be selected to induce different temperatures Allow length changes to be compensated exactly. The mechanical connections can be made very solid and thus extremely stable, since they need not absorb any mechanical deformation energy to act as an expansion buffer between the carrier and the component. Such a module can therefore have a mechanically extremely stable connection between the carrier and the component, without the functioning of the component being adversely affected by a mechanical stress. Therefore, it is also possible to design the component so thin that the requirements in terms of compactness is satisfied.

Although it could be dispensed with the compensation structure, if only a single mechanical connection between the carrier and the component exists, because then both bodies could pursue their different length extensions undisturbed. However, the mechanical connections should usually also represent electrical signal paths at the same time, so that a larger number of connections, for. B. two, three or four exist.

In the simplest case, there are two mechanical connections between the carrier and the component. In such an embodiment, the compensation structure bridges the distance Δd = d ₂ -d ₁ along the connecting direction between the two attachment points. Furthermore:

Ie. the distances d and the expansion coefficients K are chosen accordingly. There are several possibilities for this: For given coefficients of expansion (which are generally given by the choice of materials), the distances of the attachment points can be selected. In particular, it is sufficient to choose one of the two distances if the other one and the coefficients are given. Another possibility at given distances is to choose the material of the compensation structure, the material of the carrier or the material of the component according to the equation.

The meaning of the quantities and the mode of operation of the compensation structure are included in the 1 and 2 clearly displayed.

It is possible that the coefficient of expansion K _K of the compensation structure is greater than the greater of the two values K ₁ and K _2: K _K > max (K ₁ , K ₂ ) (2)

Alternatively, it is possible that the coefficient of expansion K _K is smaller than the smaller of the two values K ₁ and K. ₂ Accordingly: K _K <min (K ₁ , K ₂ ) (3)

It is also possible that the compensation structure comprises a horizontal section which is arranged on or above the carrier.

In particular, the horizontal section is used in a change in length of the carrier and the component by a separate change in length, which is adjusted accordingly, to avoid stresses. The horizontal section bridges a horizontal area and runs essentially parallel to the surface of the carrier. However, it is also possible that the horizontal section at a more or less flat angle also bridges the height difference between the top of the carrier and the bottom of the device.

In principle, a single electrical connection is sufficient, which can also be a mechanical connection at the same time, in order to forward a signal from the MEMS component to the carrier. Thus, the device could have a single floating electrode.

However, it is generally preferred to apply a voltage or a current to at least one circuit element in the component, so that a minimum number of two electrical connections is preferred. If a further mechanical connection is added and the component is supported at three points, the mechanical stability of the suspension is again significantly improved. The number of mechanical and electrical connections between the carrier and the component can still be significantly greater. Is the device z. Example, an electro-acoustic transducer and comprises a plurality of membranes or a plurality of back plates, which are to be acted upon in each case with an electric potential, so four, five or six electrical connections between the carrier and the device may be provided.

It is therefore possible for the module to include one or more additional compensation structures connecting additional attachment points of the carrier to additional attachment points of the device.

At least one of the mechanical connections, but preferably several or all mechanical connections, comprise in this case a compensation structure which, together with the other compensation structures, with a temperature change, the different changes in length of Compensated carrier and MEMS device. The individual mechanical connections and / or their compensation structures can have the same structure and be selected from the same materials. If the module has more than two compensation structures, it is no longer possible to align the compensation structures along a connecting line between two attachment points. Instead, such a module has a common center, from which the compensation structures are arranged in the radial direction. With more than two compensation structures, the dimensionality of the geometry of the arrangements of the compensation structures increases. With only two attachment points per body, the different length expansion is a one-dimensional problem. In the case of three or more compensation structures, different expansion coefficients exist in two dimensions, wherein each expansion coefficient K ₁ , K ₂ , K _{K can have} different components in the x or y direction.

If the expansion coefficients are isotropic, all compensation structures have the same structure and are arranged rotationally symmetrical about a common center, the different temperature expansion can again be attributed to a one-dimensional problem for which equation (1) holds. The sizes d ₁ and d _{2 represent} the distances of the respective attachment point of the compensation structure from the common center.

It is possible that the carrier may be a ceramic material or an organic material, e.g. B. includes a printed circuit board material and / or BCB (Benzocyclobuten).

It is also possible that the MEMS device comprises a body made of a semiconductor material, for. Si (silicon).

The carrier can have a plurality of dielectric layers, between which structured metallization layers are arranged.

It is possible that at least one compensation structure or all compensation structures comprise a metal. The metal may be, for example, Cu (copper), Ag (silver), Au (gold), Ni (nickel), or another metal that may be deposited on the top of the support by conventional material deposition processes.

It is advantageous if all compensation structures are arranged radially symmetrically about a common center. The compensation structures need not all have the same distance from the center. It is also possible for a first group of compensation structures to have a first distance and a second group of compensation structures a second distance etc. from the center. The compensation structures are then arranged in each case along imaginary circular lines around the center. A rotation of the compensation structures by a certain angle around the center then re-introduces the compensation structures into itself.

It is possible for at least one of the compensation structures or several or all compensation structures to be connected to a plurality of attachment points on the carrier and / or a plurality of attachment points on the MEMS component. Such a multi-point connection increases the resilience of the compensation structure in the event that it should detach at an attachment point of the carrier or component.

It is possible for the MEMS device to have a body with a height ≦ 700 μm and a side length between 0.3 mm and 5 mm.

Correspondingly thin MEMS components can be fastened quasi stress-free over a wide temperature range due to the above-described compensation structures and contribute to the overall height of the module in comparison with conventional fasteners significantly less.

It is possible that the MEMS device is an electroacoustic transducer. The electroacoustic transducer may comprise at least one membrane and at least one backplate, a body of silicon with a structured cavity behind the membrane and at least two electrical connections.

The module is doing a microphone, the microphone may include another chip in which z. B. an ASIC is integrated.

Such a microphone can have three or more compensation structures in the module, which are rotationally symmetrical about a center. The electroacoustic transducer also has a signal input located in the region of the center.

The material of the compensation structures can essentially comprise any material, preferably any conductive material, whose thermal expansion coefficient is smaller than the smaller of the two bodies. Then: _{d2 <d1.} Alternatively, the thermal expansion coefficient of the compensation structure may also be greater than the larger of the expansion coefficients of the bodies. Then: d ₂ > d ₁ .

Methods for developing such modules can be the optimization software TopOpt developed at the Technical University of Denmark (DTU). Especially when external constraints force a departure from a purely one-dimensional structure, eg. B. because a sound inlet opening must not be covered by the compensation structures, because the mechanical stability must be optimized with respect to particularly stringent drop tests, etc., software-based simulation tools are advantageous.

It is possible that the compensation structure is intended to elastically, that is, the MEMS device. H. springy, fasten. Then z. B. acceleration peaks and / or forces are absorbed during installation in a telephone and mechanically induced deformations are mitigated or avoided.

The module and the principles of operation of the compensation structures will be explained in more detail with reference to the schematic figures and non-limiting exemplary embodiments.

Showing:

1 : the spatial arrangement of a carrier, a component and two mechanical connections at a first temperature,

2 the same arrangement at a second temperature,

3 an exemplary conventional microphone,

4 : a section of a microphone in which an electroacoustic transducer is connected and interconnected via a compensation structure with a multilayer substrate,

5 FIG. 3: a perspective view of a module with a component connected to a carrier by mechanical connections, FIG.

6 FIG. 2: a perspective view of a compensation structure of FIG 5 .

7 a mechanical connection having a substantially one-dimensional orientation,

8th a mechanical connection with a two-dimensional orientation,

9 : a further development of the mechanical connection of the 6 with reduced voltage horizontal sections.

1 shows an arrangement of a module M with a MEMS device MB on a carrier T. The component MB and the carrier T are connected via a first mechanical connection MV1 and via a second mechanical connection MV2. The distance between the connection points on the component is d ₁ . The distance of the connection points on the carrier T is d ₂ . At a certain temperature, the device has a length l ₁ and the carrier has a length _L2.

If the dimensions and the materials are selected accordingly, there is a complete compensation of the linear expansion and thus a complete avoidance of thermally induced stresses in the entire temperature range, in which the materials expand linearly with a temperature change.

2 shows the same structure at a temperature that is around a differential temperature .DELTA.T from the temperature of in 1 differs shown situation. The length of the device MB is grown from l ₁ to l _-1. The distance between the attachment points on the component has increased from d ₁ to d ₁ ': d ' ₁ = d ₁ + d ₁ K ₁ ΔT = d ₁ (1 + K ₁ ΔT) (4)

The distance between the attachment points on the support has increased from d ₂ to d ₂ ': d ' ₂ = d ₂ + d ₂ K ₂ ΔT = d ₂ (1 + K ₂ ΔT) (5)

Is the distance of the attachment points at the temperature of 1 still Δd: Δd = d ₂ -d ₁ (6), so the distance grows to Δd ': Δd '= d' ₂ - d ' ₁ (7)

The second mechanical connection MV2 has a compensation structure KS with a horizontal section HA, which bridges the length difference Δd or Δd '. Relative to the distances d, the material of the compensation structure KS or its horizontal section HA is chosen so that the different linear expansion Δd '- Δd is compensated. For a linear expansion, the following applies: Δd '= Δd (1 + K _× ΔT) (8)

From (4) and (5) follows: Δd '= Δd + (d ₂ K ₂ -d ₁ K ₁ ) ΔT (9)

From (8) and (9) follows: Δd (1 + K _K ΔT) = Δd + (d ₂ K ₂ -d ₁ K ₁ ) ΔT (10)

It follows: ΔdK _K = d ₂ K ₂ -d ₁ K ₁ (11)

From equation (11) equation (1) results directly.

If the carrier T has a larger temperature expansion coefficient than the MEMS component MB, then d ₂ > d ₁ . In the opposite case (K ₁ > K ₂ ) d ₁ > d ₂ would have to be or the thermal expansion coefficient of the compensation structure KS be smaller than the thermal expansion coefficient of the carrier T. Instead of a compensation structure with a small coefficient of thermal expansion, the construction can be reversed.

3 shows a section of a conventional microphone, in which an electroacoustic transducer EAW is connected via bump connections BU with a multi-layer substrate MLS and interconnected. In addition to the electroacoustic converter EAW, a chip with an ASIC is arranged on the multilayer substrate MLS. Different coefficients of expansion of the multilayer substrate, converter EAW and chip ASIC disturb the functionality of the converter EAW significantly more than the generally exclusively electrical functionality of the chip ASIC. Because the converter is more sensitive to mechanical stresses than the chip ASIC.

4 shows a corresponding improvement of the microphone, in which the electroacoustic transducer, here with a membrane ME and a back plate BP via a bump connection is not connected directly to the multilayer substrate MLS, but with a compensation structure KS and interconnected. At the point which is provided for connection to the solder material, a solder pad may be arranged. Analogously, the converter EAW can also have solder pads, so that a permanent solder connection can take place.

5 shows a perspective view of a module M, in which a MEMS component MB disposed on a support T and connected via mechanical connections or their compensation structures KS and interconnected. The module comprises four mechanical connections, which are rotationally symmetrical about their common center Z arranged and aligned. Each of the mechanical connections has four contact points with the carrier T and one contact point with the component MB.

In the region of the center Z, the component MB has a sound inlet opening. In this case, the mechanical connections MV are grouped around the sound inlet opening so that an acoustic signal can be received without difficulty.

6 shows a mechanical connection of 5 in perspective view. The mechanical connection has four mounting points BP-T, with which it is attached to the carrier. Furthermore, the mechanical connection has an attachment point BP-MB, via which it is connected to the MEMS component. The mechanical connection further comprises horizontal sections HA which allow length compensation in two dimensions.

The horizontal portions HA can be slightly raised relative to the attachment points on the carrier BP-T, so that no mechanical stresses between the horizontal sections HA and the carrier T can form.

Such mechanical connections can be made during the manufacturing process by applying the horizontal portions HA to a sacrificial material on the carrier T, which is removed after application of the material of the horizontal portions HA.

7 shows a substantially one-dimensional mechanical connection having exactly one attachment point on the carrier BP-T and exactly one attachment point for the MEMS device BP-MB. A horizontal section between them connects the two points.

8th shows an embodiment of a mechanical connection having horizontal portions in two directions. Accordingly, there are two attachment points BP-T to the carrier and an attachment point BP-MB to the device.

The horizontal sections are here - in contrast to the embodiment of 7 - Not by sections with rectilinear edges, but designed by sections with curved edges to avoid mechanical stress concentrations. According to shows 9 an embodiment of a mechanical connection with four attachment points BP-T to the support and an attachment point BP-MB to the device, wherein the horizontal portions HA are also configured by sections with curved edges.

The module is not limited to the embodiments shown. Modules with further mechanical and / or electrical connections for temperature compensation or modules with further components also represent realizations according to the invention.

LIST OF REFERENCE NUMBERS

ASIC

ASIC chip

BP

backplate

BP-MB

Attachment point to the component

BP-T

Attachment point to the carrier

BU

Bump connection

d ₁

Distance of the attachment points on the MEMS component or distance of the attachment points on the MEMS component from the center

d ₂

Distance of the mechanical connections on the support or distance of the attachment point of the mechanical connection from the center to the support

EAW

electroacoustic transducer

HA

horizontal section

K ₁

Temperature expansion coefficient of the carrier

K ₂

Temperature expansion coefficient of the device

K _K

Temperature expansion coefficient of the compensation structure

KS

(Temperature) compensation structure

₁

Length of the MEMS device

l ₂

Length of the carrier

M

module

MB

MEMS component

ME

membrane

MLS

Multilayer substrate

MV

mechanical connection

MV1, MV2

first, second mechanical connection

T

carrier

Z

(Symmetry) center

Δd, Δd '

to be bridged by the compensation structure horizontal distance

Claims (17)

Electric module (M), comprising - a carrier (T) having a first temperature expansion coefficient K ₁ , a first attachment point and a second attachment point, - a MEMS device (MB) with MEMS structures (ME, BP), a second one Temperature expansion coefficients K ₂ ≠ K ₁ , a first attachment point and a second attachment point, - a first mechanical connection (MV1) between the first attachment point of the carrier (T) and the first attachment point of the component (MB), - a second mechanical connection ( MV2) (between the second fastening point of the carrier (T) and the second attachment point of the device MB) with a compensation structure (KS) with a temperature coefficient of expansion K _K, wherein - the attachment points on the MEMS device (MB) by a horizontal distance d ₁ and the attachment points on the support (T) have a horizontal distance d ₂ , - the values for d ₁ and d ₂ are chosen such that the compensation structure (KS) at a temperature change, the different changes in length d ₁ and d ₂ compensated by their own caused by the change in temperature change in length, and the MEMS device (MB) is connected at different temperatures without voltage to the carrier. Electric module (M), comprising - a carrier (T) having a first temperature expansion coefficient K ₁ , a first attachment point and a second attachment point, - a MEMS device (MB) with MEMS structures (ME, BP), a second one Temperature expansion coefficients K ₂ ≠ K ₁ , a first attachment point and a second attachment point, - a first mechanical connection (MV1) between the first attachment point of the carrier (T) and the first attachment point of the component (MB) with a compensation structure (KS) a temperature expansion coefficient K _K , - a second mechanical connection (MV2) between the second attachment point of the carrier (T) and the second attachment point of the component (MB) with a compensation structure (KS) with a coefficient of thermal expansion K _K , wherein - the Attachment points on the MEMS device (MB) a horizontal distance d ₁ and the attachment points on the support (T) a n horizontal distance d ₂ , - the values for d ₁ and d ₂ are chosen such that the two compensation structures (KS) compensate for the different changes in length of d ₁ and d ₂ due to their own changes in length due to the temperature change, and the MEMS device (MB) is connected at different temperatures without voltage to the carrier. Module according to one of the preceding claims, wherein - the one or the two compensation structures (KS) bridge the distance Δd = d ₂ - d ₁ along the connecting direction between the two second attachment points and - the equation d ₂ = d ₁ (K _K -K ₁ ) / (K _K - K ₂ ) is satisfied. Module according to one of the preceding claims, wherein K _K - either greater than the larger of the two values K ₁ and K ₂ is: K _K > max (K ₁ , K ₂ ) or - smaller than the smaller of the two values K ₁ and K ₂ is: K _K <min (K ₁ , K ₂ ). Module according to one of the preceding claims, wherein the compensation structure (KS) comprises a horizontal portion (HA), which is arranged on or above the carrier (T). Module according to one of the preceding claims, further comprising one or more additional compensation structures (KS), the additional attachment points of the carrier (TS) with additional attachment points of the MEMS device (MB) connect. Module according to one of the preceding claims, in which at least one compensation structure (KS) forms an electrical connection between carrier (T) and MEMS component (MB). Module according to one of the preceding claims, wherein the support (T) comprises a ceramic material or an organic circuit board material. Module according to the preceding claim, wherein the carrier (T) comprises a plurality of dielectric layers, between which structured metallization layers (ML) are arranged. Module according to one of the preceding claims, wherein the MEMS device (MB) comprises a body made of a semiconductor material. Module according to one of the preceding claims, wherein at least one compensation structure (KS) comprises a metal. Module according to one of the preceding claims, wherein all compensation structures (KS) are arranged radially symmetrically about a center (Z). Module according to one of the preceding claims, wherein at least one compensation structure (KS) with a plurality of attachment points on the carrier (T) and / or with a plurality of attachment points on the MEMS device (MB) is connected. Module according to one of the preceding claims, wherein the MEMS device (MB) has a body with a height ≤ 700 microns and with a side length between 0.3 mm and 5 mm. Module according to one of the preceding claims, wherein the MEMS device (MB) is an electroacoustic transducer (EAW). Module according to the previous claim, wherein - The module (M) has three or more compensation structures (KS) which are rotationally symmetrical about a center (Z) are arranged, and - The electroacoustic transducer (EAW) comprises a sound input in the center (Z). Module according to one of the preceding claims, wherein the compensation structure (KS) is provided to fix the MEMS component (MB) elastically.

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